This invention relates in general to communication equipment, and more specifically to an improved adjustable gain control system, an integrated circuit amplifier using such system, and methods thereof.
Communications equipment such as receivers and transmitters that use or require gain control are known. Due to the wide variety of communications systems defined by various standards and deployed by various carriers and the desire to field equipment that operates in a plurality of these systems the demands or requirements for adjustable gain control approaches and systems have grown. Many of present and planned systems are designed to be interference limited. In such systems signal levels need to be as closely controlled as practical. In the end that means that the gain or amplification of signal processing line-ups used in equipment deployed in such systems is also critical. Thus requirements for the accuracy and repeatability of adjustable gain control systems have become more stringent. At the same time size and cost pressures on the equipment as well as complexity of the equipment mandate the use of as much integrated functionality as possible.
Thus most adjustable gain control systems and many amplifiers whose gain must be controlled are in integrated circuit form. Many of these gain control systems have various forms of compensation for some performance variables, such as large signal current gains and for some environmental variables such as temperature. However known gain control systems have suffered from inaccuracies due to random mismatches of process variables and mismatches due to process gradients. Thus known systems have suffered with respect to repetitively providing known predetermined levels of gain control over multiple gain settings and across multiple copies of the same system. Clearly a need exists for an improved adjustable gain control system and methods thereof.
This invention concerns communications equipment and improved apparatus and methods for adjustable gain control. In one aspect the invention is an adjustable gain control (AGC) system with improved gain control accuracy for an analog amplifier. The AGC system includes an offset circuit for providing an offset signal that is selectable; a gain setting source for providing a gain set signal that is dependent on a gain select signal and the offset signal; and an AGC circuit, coupled to the offset signal and the gain set signal, for providing a gain control signal for the analog amplifier, the AGC circuit compensating, according to the offset signal, the gain control signal for process variables corresponding to the AGC circuit to provide a plurality of predetermined gains for the amplifier that correspond, respectively, to a plurality of gain select signals.
In a further aspect the invention is an integrated circuit amplifier having an adjustable gain control characteristic where the integrated circuit includes a low noise amplifier (LNA) having a gain control input coupled to a gain control signal for amplifying an input signal according to the gain control signal to provide an output signal; and a gain control system with adjustable gain control (AGC) for providing the gain control signal. The gain control system includes an offset circuit for providing an offset signal that is selectable; a gain setting source for providing a gain set signal that is dependent on a desired gain and the offset signal; and an AGC circuit, coupled to the offset signal and the gain set signal, for providing the gain control signal for the LNA, the AGC circuit compensating, according to the offset signal, the gain control signal for process variables corresponding to the AGC circuit to provide a plurality of predetermined gains for the amplifier that correspond, respectively, to a plurality of gain select signals indicative of a plurality of respective desired gains.
A method aspect of the invention is a method in an adjustable gain control (AGC) system of providing improved gain control for an analog amplifier. The method includes providing an offset signal that is selectable; providing a gain set signal that is dependent on a desired gain and the offset signal; and generating, responsive to the offset signal and the gain set signal, a gain control signal for the analog amplifier, and compensating, according to the offset signal, the gain control signal for process variables corresponding to the AGC system to provide a plurality of predetermined gains for the amplifier that correspond, respectively, to a plurality of gain select signals.